1. Field of the Invention
This invention relates to the removing of dispersed contaminants from fluids. It more particularly relates to a method of testing fibrous coalescer elements for their ability to remove emulsified water initially present from hydrocarbon fuels, lubricating oils and other similar organic fluids, which in addition to water may contain other impurities such as water soluble surfactants and inorganic solids. It also relates to a method of testing fibrous coalescer elements for their ability to coalesce oil from oily water.
2. Description of the Prior Art
It is frequently necessary to remove liquid contaminants such as water or solutions of salt from fuels or other petroleum distillates if they are to be suitable for their intended use. For example, emulsified water droplets in aircraft fuels may freeze forming ice crystals which could plug fuel lines, interrupting the flow of fuel to the engine. Further, gross quantities of water carried in the fuel stream may cause engine failure or malfunction, and indeed could cause loss of the aircraft. When the entrained water contains dissolved salts, corrosion of fuel system components may also result. In addition, water or aqueous solutions of salt in hydraulic fluids or other types of petroleum products, including lubricating oils could cause similar problems along with corrosion of the system components. Removal of oil from oily waste water such as bilge water or ballast water on shipboard is required before discharge of the waste water into the waterway or coastal water is legally permissible. Techniques for cleaning up oily waste water prior to discharge have been developed. Various means have been employed heretofore to remove such liquid contaminants; however, a particular problem exists when one attempts to remove water from an emulsion of the same and fuel oils, lubricating oils and the like.
In accordance with one prior technique, the contaminated fluid or fuel is passed through an electric field which is employed as a means of causing coalescence of dispersed aqueous contaminants thereby facilitating their removal from the fluid stream by gravity separation or other mechanical means.
A disadvantage of the electric type of coalescer is that the electrodes must be relatively widely spaced to avoid shorting where other than small amounts of water are present in the oil. In addition, they require a source of electrical energy for their operation, and when the fluid is flammable there always exists the hazard of an explosion in the event of an electrical short. Further, such devices have a relatively high initial cost and require a skilled operator for their maintenance and operation.
Another method of removing such aqueous impurities from oil or oily impurities from water are mechanical filters sometimes described as filter/separators or alternatively, fibrous coalescer elements. These devices have the advantage of not requiring electrical power for their operation or skilled operators. However, they do suffer from one disadvantage. Specifically, if the surface of the elements are contacted or contaminated with a surface active material, their effectiveness of coalescing are substantially reduced or possible totally eliminated. During the manufacture of the elements and their assembly, it is not uncommon for some of the elements to become contaminated with surface active agents to such a degree that they are unacceptable for their intended purpose. Hundreds of thousands of such fibrous coalescer elements are bought annually by the various Department of Defense agencies. These elements are supposed to conform to certain military specifications, for example MIL-F-52308, in their ability to coalesce free water from petroleum fuels, or to MIL-S-52846 in their ability to coalesce oil from oily waste water. In practice, however, it has been reported that individual lots of such elements are often found not to perform as expected. Indeed, it has been reported by certain authorities that in practice defective elements sometimes constitute as much as 30% of the accepted manufacturer's lots. This is believed to result from the types of screening presently available. Specifically, the various lots of coalescer elements are subjected to random sampling, with individual selected elements being utilized to filter and coalesce water from contaminated fuels. The effluent is then chemically analyzed for water and particulate component concentration to determine the effectiveness of that particular element. However, since the fuels also frequently contain surfactants as impurities, the elements become contaminated during testing and are seldom useable thereafter for their commercially intended purpose.
It also will be appreciated that in random sampling, the probability of the sample reflecting the true acceptability of the total lot will depend upon the size of sample taken; i.e., the larger the sample size, the larger the probability that it is truly representative of the lot. However, it conversely follows that the larger the sample size, the fewer elements remain for use for their intended purpose. Clearly, therefore, there exists a need for an improved method of testing such fibrous coalescer elements, to determine their acceptability for use either in removing or separating water from various petroleum products.